#game {
    width: 100%;
    height: 600px;
    background: url(../images/sky.png);
    /* 更改background-position-x 可以使背景图片移动 */
    background-position-x: 0px;
    position: relative;
    overflow: hidden;
}

.bird {
    position: absolute;
    width: 30px;
    height: 30px;
    background: url(../images/birds.png);
    left: 50%;
    margin-left: -15px;
    top: 235px;
    /* 过渡效果，top改变触发过度效果， linear表示匀速 */
    transition: top .3s linear;
}

.start {
    width: 200px;
    height: 60px;
    position: absolute;
    left: 50%;
    margin-left: -100px;
    top: 295px;
    line-height: 60px;
    text-align: center;
    font-weight: bolder;
    transition: all .3s linear;
    cursor: pointer;
}

.start.start-white {
    color: #fff;
    font-size: 24px;
}

.start.start-blue {
    color: #09f;
    font-size: 36px;
}

.score {
    position: absolute;
    text-align: center;
    left: 50%;
    /* transform: translateX(-50%)可以在不知道宽的情况下，达到水平居中 */
    transform: translateX(-50%);
    font-size: 20px;
    font-weight: bolder;
    color: #fff;
    display: none;
    z-index: 1;
}

.mask {
    position: absolute;
    /* 下面的效果能达到背景平铺父级 */
    top: 0;
    left: 0;
    bottom: 0;
    right: 0;
    background-color: rgba(0, 0, 0, .7);
    display: none;
    z-index: 2;
}

.end {
    position: absolute;
    left: 50%;
    transform: translateX(-50%);
    top: 70px;
    display: none;
    text-align: center;
    z-index: 3;
}

.end .over {
    color: red;
    font-weight: bolder;
    font-weight: 36px;
}

.end .results,
.end .final-score {
    margin-top: 20px;
    font-size: 20px;
    font-weight: bold;
    color: #ff0;
}

/* 排行榜列表 */
.end .rank-list {
    color: #09f;
    margin-top: 20px;
}

.end .rank-list .rank-item {
    height: 30px;
    line-height: 30px;
    margin-bottom: 10px;
    font-size: 14px;
}

.end .rank-list .rank-item .rank-degree {
    display: inline-block;
    width: 14px;
    height: 14px;
    line-height: 14px;
    font-size: 12px;
    color: #fff;
    background-color: #8eb9f5;
    margin-right: 10px;
}

.end .rank-list .rank-degree.first {
    background-color: #f54545;
}

.end .rank-list .rank-degree.second {
    background-color: #ff8547;
}

.end .rank-list .rank-degree.third {
    background-color: #ffac38;
}

.end .rank-score {
    width: 30px;
    display: inline-block;
}

.end .restart {
    color: #09f;
    font-size: 18px;
    font-weight: bolder;
    cursor: pointer;

}

.pipe {
    position: absolute;
    /* 将固定不变的样式在CSS内写 */
    width: 52px;
    /* background-color: red; */
}

.pipe.pipe-up {
    top: 0;
    background-image: url(../images/pipe2.png);
    background-position-y: bottom;
}

.pipe.pipe-down {
    background-image: url(../images/pipe1.png);
    bottom: 0;
}